1. Field of the Invention
The present invention relates to a method of and an apparatus for packet-rate control of arrival packets in packet networks, and in particular to rate control intended for packets (violation packets) transmitted excessively from a subscriber terminal device in violation of a contract closed between a network provider and a subscriber or user in packet networks using an ATM (Asynchronous Transfer Mode).
2. Description of the Related Art
As a promising communication method of the next generation, ATM networks for transferring information in the form of fixed-length packets (hereafter referred to simply as "cells") are now being studied in various research institutions. In ATM networks, communication of information (such as speech, image or data) generated from various kinds of media and having various transfer speeds is performed.
In general, there is a limit in communication capacity which can be provided by a network. When a terminal device requests a call, therefore, the network provider makes the subscriber (or the terminal device) declare parameters such as bit rate and determines whether the quantity of cells passing through the network exceeds the communication capacity as a result of cells newly generated when that call request is admitted. If the quantity of the cells passing through the network is judged not to exceed the communication capacity, the above described call request is admitted. If the subscriber transmits cells excessively in violation of the user-declaring parameters, however, the quantity of cells passing through the network exceeds the communication capacity, resulting in degradation of quality of service such as loss of some cells caused by discarding excess cells or an increase of delay time in cell transfer and exchange.
In ATM networks, a plurality of subscribers performs communication by sharing the same resources (such as transfer nodes and links). If some subscriber transmits a large number of cells in violation of user-declaring parameters, therefore, it influences other subscribers which do not violate user-declaring parameters as degradation in quality of service. Therefore, it becomes necessary to exercise packet-rate control for regulating cells transmitted in violation of user-declaring parameters (hereafter referred to as "violation cells".)
As the above described packet-rate control method for violation packets, there are heretofore known
(1) a method of discarding all violation cells, and
(2) a method of adding a special mark indicating violation to violation cells and discarding cells having the above described mark added thereto (hereafter referred to as "marked cells") when congestion has occurred in the network. These packet-rate control techniques are described in Toshio Suzuki et al., "Configuration of the Broadband Subscriber Interface Unit", The Institute of Electronics, Information and Communication Engineers Technical Report SSE89-148, pp. 13-18 for example.
In the conventional method (1) of discarding all violation cells, however, violation cells are immediately discarded even if the quantity of cells passing through the network is sufficiently smaller than the communication capacity. In such a period that there is a margin of communication capacity, communication resources are not used efficiently, resulting in a problem.
In the conventional method (2) of discarding marked cells, violation cells are received in the network without any restriction, and regulation for marked cells is not performed unless congestion has actually occurred. In case a large quantity of violation cells are sent into the network as a result of disorders in some subscriber terminals, for example, therefore, congestion is generated in the network by these violation cells (marked cells) and a bad influence is exerted upon the quality of service of other subscribers maintaining communication while obeying the user-declared parameters, resulting in a problem.
In these conventional control methods, means for notifying the subscriber of terminal disorder is not provided. Until the subscriber notices the terminal disorder by itself, therefore, the disordered terminal continues to transmit violation cells for a relatively long term, resulting in a problem.